1. Field of the Invention
This invention relates to a concrete arch buried bridge.
2. Description of the Prior Art
Examples of such structures are shown in Canadian Pat. Nos. 749,630, Fisher (1967), 804,292, Fisher (1969), 1,143,170, Peterson (1983) and U.S. Pat. No. 3,508,406, Fisher (1971).
Some of these structures are supported by footings which, in turn, rest in the ground on a permanent natural bed. Other types have no footings, but merely buttresses, capable of carrying only horizontal stresses. A further type is provided with laterally extending arms which receive support from underlying compacted fill as well as support from a bottom lining of the conduit.
The type of concrete arch buried bridge to which the present invention relates is one which employs a lower part or lining which rests on a fill and an upper part or lining connected to it. The upper part has a reinforced concrete cap connected to it. Usually a connection is made between the upper part and a lower part at their lateral margins to form a conduit prior to application of any load to the upper part.
A disadvantage of this type of structure is that the upper part tends to settle, following its construction, more than does the lower part. This stresses the lower part, primarily adjacent its lateral margins, where the structure is weakest. So without special protective measures this stress could be ultimately lead to localized failure. Attempts have been made to overcome this by providing a well compacted select granular fill so as to reduce settling to a minimum. However, this is uncertain, because, among other things, the moisture content of the fill can fluctuate.
Having regard to the foregoing, it is an aim of the present invention to provide a construction which avoids these disadvantages and provides certain positive advantages as will be evident from the following description.